The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Conventionally and as illustrated in FIG. 1, a nacelle 1 may be attached to a fixed structure SF of an aircraft or airplane, such as a wing, via a pylon or mast 2. The nacelle 1 has a structure comprising an air intake section 3 upstream, a middle section for surrounding a fan (not visible) of the turbojet engine, and a downstream section 5 surrounding the turbojet engine and harboring a thrust reverser 50.
The middle section 4 includes a case 41, a so-called fan case, attached at its upstream end to the air intake structure 3 and at its downstream end to the downstream section 5 and thus to the thrust reverser 50; this fan case 41 being surrounded by an external fan cowl 40. The fan case 41 is directly attached on the upstream portion 21 of the pylon 2, while the downstream portion 22 of the pylon 2 is attached on the wing SF. The downstream section 5 further includes an internal structure (not visible) surrounding the turbojet engine and partly defining a ring shaped vein for letting through an airflow, this internal structure delimiting an internal line of this ring shaped vein.
For reasons of mass and of congestion with the external aerodynamic lines of the nacelle 1, the pylon 2 has in its upstream portion 21 a relatively thin or not very thick structure, comparatively with its downstream portion 22.
As illustrated in FIG. 2, in the majority of applications on airplanes and notably in applications of a turbojet engine under a wing, the thrust reverser 50 comprises a cowl defining with the internal structure the ring shaped vein, this cowl delimiting an external line LE (visible in FIG. 3) of this ring shaped vein. Conventionally, the thrust reverser 50 in the closed position is maintained on the downstream end of the fan case 41 by a knife system inserted in a groove (not illustrated).
The cowl of the thrust reverser 50 includes two removable half cowls 51 respectively having upper edges 52 equipped with means 53 for jointing the half-cowls 51 on the pylon 2. These jointing means 53 are shaped so as to allow pivoting of the half-cowls 51 between closed and open positions around respective longitudinal axes forming hinge lines LC. Conventionally, the joint of the half-cowls 51 on the pylon 2 is made by means of floating connecting rods 53 which define the hinge lines LC.
Both half cowls 51 also have free lower edges 54, opposite to the upper edges 52, which are generally provided with lower locking means (not illustrated such as for example a lock or hook system) designed so as to keep the half cowl 51 closed in the lower portion of the nacelle 1 (at 6 o'clock). These lower locking means may for example be actuated by a lower locking handle positioned on one of the lower edges 54 and movable between a locking position and an unlocking position for the lower locking means.
The arrangement of the hinge lines LC allowing the opening of the half cowls 51 required for maintenance operations, should, in a wide upstream portion of the half-cowl 51, not interfere with the hooking up of a thrust reverser 50 on the fan case 41, with the risk of having a hyperstatic assembly and thereby generating parasitic and detrimental stresses between the thrust reverser 50 and the fan case 41.
In order to rigidly bind the half cowls 51 to each other without interfering with the upstream hooking up of the half cowls 51 on the fan case 41, the floating connecting rods 53 are installed through the pylon 2, downstream from the upstream portion 21 (as is visible in FIG. 3) wherein the pylon 2 is sufficiently thick for supporting a structural failure induced by the openings crossed by the connecting rods 53. The floating connecting rods 53 are conventionally mounted with play through the pylon 2, in order not to interfere during relative movements of the different structures of the nacelle 1.
Now, in the case of a substantial displacement of the nacelle, there exists a risk of detaching the hooking up of the half cowls of the thrust reverser on the fan case, as this may be observed in a situation of fan blade breakage which generates very large displacements of the nacelle due to the unbalance generated by the off-balance of the shaft of the turbojet engine.
The state of the art may be illustrated by the teaching of document U.S. Pat. No. 4,679,750 A which discloses a nacelle including an upper safety system (upper latch assembly) which connects together the upper edges of the half cowls of the thrust reverser and which is shaped in order to lock these half cowls in the closed position when it occupies a locking configuration and for allowing opening of the half cowls when it occupies an unlocking configuration.
However, this upper safety system is also attached to the two external fan half cowls (fan cowl) via a connecting rod slidably mounted in the groove of a guide mounted on the external fan half cowls. Thus, this upper safety system gives the possibility of opening the half cowls of the thrust reverser only when the external fan half cowls are open.